


A Secret Lesson

by raregloves



Category: Sherlock (TV)
Genre: However do NOT read if any kind of underage bothers you, M/M, Moral Ambiguity, Morally Ambiguous Character, POV Mycroft Holmes, Set over many years, Sibling Incest, This does end up being a loving relationship, Underage Mycroft (to some extent), Underage Sherlock, pre-ASiP
Language: English
Status: Completed
Published: 2014-06-24
Updated: 2014-06-24
Packaged: 2018-02-06 01:41:23
Rating: Explicit
Warnings: Underage
Chapters: 1
Words: 2,959
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/1839685
Author URL: https://archiveofourown.org/users/raregloves/pseuds/raregloves
Summary: <blockquote class="userstuff">
              <p>Sherlock had always had a remarkable ability to manipulate the people around him. Especially the people who loved him.</p>
            </blockquote>





	A Secret Lesson

**Author's Note:**

> Prompt: Could you maybe please write a love-y Holmescest fic? Errr... and please don't think I'm a huge freak for this (though, maybe I am) could there be some under-age-y-ness? I just really like the idea of Sherlock ALWAYS being in love with his brother, and always having his super gift of manipulation, so he can get Mycroft to do whatever he wants.

Mycroft took his little brothers hand as they walked towards the pond at the edge of the garden. It was a bright, windy day and the grass felt springy under his bare feet.  
  
Beside him, Sherlock was nearly skipping with excitement. He wanted desperately to examine the life forms growing in the pond, and was tugging Mycroft forward, trying to drag him. He was strong for a seven year old, Mycroft thought.  
  
‘Tadpoles!’ Sherlock shouted. ‘And frogs and fish and mostioqos!’  
  
‘Mosquito,’ Mycroft said. ‘And I don’t know if we’ll see any tadpoles, Sherlock.’  
  
‘I love learning things with you,’ Sherlock said, beaming up at Mycroft. ‘You’re so smart.’  
  
Mycroft smiled, pleased. None of his classmates appreciated intelligence in the same way his brother did. They were concerned with kissing, and competing about who had watched the most explicit movies. Sherlock was holding a basket containing a number of jars in his other hand.  
  
They reached the edge of the pond. Sherlock let go of him to rush forwards, jars clinking. He wasn’t allowed near the pond without supervision. Mycroft, who had no desire to stand in the mud, found a nearby tree and sat at the base on a surprisingly comfortable root.  
  
He watched Sherlock investigate the pond, enjoying the sun on his face and the cool touch of the wind. Sherlock splashed about, collecting all kinds of things in his jars: worms, beetles, moss…  
  
Mycroft fell into a slight doze, lulled by the peacefulness of the day. But he kept his ears open, in case something happened to Sherlock. Even the smartest child could drown, after all.  
  
But he must have fallen asleep. Because he woke with a start, some time later, to the feeling of Sherlock pressing against his chest. His brother was nearly covered in mud and clearly exhausted. He tucked his dark, curly head under Mycrofts chin, breathing deeply.  
  
Feeling affectionate, Mycroft ran his hand up and down Sherlocks back, soothing him. They would probably be horribly sunburnt if they stayed, but Mycroft didn’t have the heart to move him.

 

~

 

‘But Mycroft,’ Sherlock yelled. ‘I don’t know! I just want to know!’

Mycroft was desperately glad that their parents were not home to witness this (mortifying) argument. He was quite sure he had never been so embarrassed in his life.  
  
‘You can read about it in books,’ Mycroft said. ‘You don’t need me to… show you anything.’  
  
‘You told me to know everything,’ Sherlock accused. ‘And now I’m trying to and you’re not letting me because you’re mean and I hate you.’  
  
‘You don’t hate me, Sherlock,’ Mycroft said, leaning down to put his hands on Sherlocks shoulders. ‘You’re just upset that you have to follow the rules.’  
  
‘What rule?’ Sherlock looked up at him, his face stained with tears, his blue eyes watery under the shock of dark hair that stood out so fetchingly against the pale of his skin. ‘I never heard of no rule.’  
  
‘Of any rule,’ Mycroft corrected. ‘It’s just… one of the rules.’  
  
‘But we hate the rules at school,’ Sherlock said, still failing to understand. ‘You say the rules are dumb and they are. You just want to follow this rule because you hate me now.’ 

‘I don’t- Sherlock-’ Mycroft tightened his grip on Sherlocks shoulders. The idea that Sherlock thought Mycroft hated him- it broke his heart, made guilt bubble up inside his chest. ‘Sherlock. It just isn’t a good idea. I mean, why not look at yourself?’  
  
‘That’s not the same and you know it,’ Sherlock said, sniffing. ‘You’re older. You probably know all about this stuff.’  
  
‘Well, yes,’ Mycroft said. ‘But that doesn’t mean-’

Sherlock was crying again, big fat tears running over his round cheeks. Mycroft felt his heart twist.  
  
‘But I r-really loved l-l-learning things w-with you,’ Sherlock sobbed. ‘You’re the c-cleverest person I know, Myc- _hic-_ Mycroft.’  
  
‘I’m sorry, I’ll do it,’ Mycroft heard himself say. ‘It’s fine, I do love you, it’s ok. Just… don’t tell anyone, ok? It’s a secret lesson. Do you understand? A secret lesson. Just this once.  
  
‘A secret lesson?’ Sherlock said, gazing up at him. His smile was radiant and beautiful despite the redness of his eyes. ‘Thank you, Mycroft! Thank you thank you thank you!’ 

Sherlock launched himself at Mycroft, wrapping his thin arms around his middle. Smiling, Mycroft peeled him off, picking up the heavy anatomy book in his hands. It would be twenty minutes before their parents were home. 

‘Come into my room,’ Mycroft said. ‘We’ll do it in there, very quick. Ok?’  
  
‘Ok!’  
  
They climbed the stairs into Mycrofts room, Sherlock almost skipping. Mycroft felt himself smile despite his nervousness.  
  
He locked the door behind them, just in case their parents arrived home early. His heart was hammering inside his chest, almost painfully, but he looked at Sherlocks keen face and knew he would go through with it.  
  
‘Ok,’ he said, trying to take charge of the situation. ‘Open the book to the anatomy. Head to toe. We can look at where bones are, and muscles, and where my organs are, all of it.’ 

Sherlock opened the book to the required chapter. His reading skills were advanced, but Mycroft thought the pictures helped as much as the index did in this case. There was no mistaking the drawings for anything other than what they were, after all.  
  
He stripped off, blushing, feeling Sherlocks gaze on him. He had never felt quite so pale, or awkward, or chubby before. But it didn’t seem to matter to Sherlock, who was gazing at him with wide, wide eyes.  
  
‘You’re got hair!’ Sherlock accused, pointing to Mycrofts groin. ‘I don’t have any of that.’  
  
‘You will, when you get older,’ Mycroft said. Sherlock nodded seriously.  
  
‘It looks a bit curly,’ Sherlock said. ‘Curly like my hair. Can I touch it?’  
  
Mycroft hesitated, but it was too late- Sherlocks hand shot out and ran through his public hair. He had a fair bit of it now, and Sherlock tugged at it before letting go.  
  
He felt himself blush, and desperately hoped that Sherlock didn’t notice.  
  
‘So will I look like this when I get older?’ Sherlock asked.  
  
‘A bit,’ Mycroft said. ‘You’ll probably look better than I do.’  
  
‘Better?’ Sherlock gaped. ‘Than you? You’re the best though.’  
  
‘Better looking, then,’ Mycroft said, smiling, but Sherlock shook his head firmly.  
  
‘I won’t be better looking,’ he said firmly. ‘You’re the best looking.’  
  
Mycroft laughed and Sherlock ignored him, turning the pages of the book and flicking through them, his expression thoughtful.  
  
‘Can we start with muscles?’  
  
‘Yes,’ Mycroft said, feeling himself settle into teaching mode. ‘Let’s begin…’  
  
~  
  
Even though he was too old to be frightened by storms, Mycroft couldn’t help the leap in his stomach as another round of thunder sounded over the house. He could hear the windows shaking.  
  
A branch had fallen on the shed, crushing it. Father was outside, in a hardhat and raincoat, trying to assess the damage while their mother held a touch up, trying to shout instructions over the howling of the wind.  
  
Occasionally lightening would light up his room with an eerie blue glow. Mycroft pulled his covers up until they were under his chin. He wished his parents were safe inside.  
  
He heard his door open and knew without looking who he would see there. Sherlock, eleven years old not a week ago, in his blue pajamas. Sherlock always pretended he wasn’t afraid of anything during the daytime. Mycroft knew better though. His brother was afraid of many, many things.  
  
‘Can I get in? Mycroft?’  
  
Sherlocks voice was small, pleading.  He didn’t want to say yes, not really. He just wanted to sleep, to get through the storm without worrying about his parents or his brother or the house. He sometimes resented the expectations people had of him. The oldest child, the smart one.  
  
‘Please?’  
  
But Sherlocks voice sounded so small. With a sigh Mycroft lifted his blankets. Sherlock rushed over and burrowed in right away, his warm body wrapping around Mycrofts.  
  
‘Are you afraid of the storm, Mycroft?’  
  
‘No, not really.’  
  
‘Me neither,’ Sherlock boasted.  
  
The wind threw a branch against Mycrofts window with a loud crack. Sherlock screamed, hiding his face in Mycrofts neck. His curls tickled his skin, but it seemed unkind to push him away.  
  
‘It’s ok,’ Mycroft said, soothing Sherlock. ‘It’ll pass.’  
  
‘You’re so brave,’ Sherlock said. ‘You know I love you?’  
  
‘Yes, I know,’ Mycroft said, surprised. It wasn’t like Sherlock to ask questions he already knew the answer to. Not unless he had some very good point to make.  
  
‘Good,’ Sherlock said. ‘And you love me back?’  
  
‘Yes, naturally,’ Mycroft said.  
  
 Sherlock wriggled up until they were nose to nose. Lightening briefly illuminated him, making his pale skin look almost transparent for a handful of seconds. Mycroft blinked.  
  
In the following darkness Sherlock pressed his lips against Mycrofts. It might have been a chaste kiss. Should have been a chaste kiss. But as Mycroft gently pushed Sherlock back onto the bed (‘Sleep now, Sherlock…’) he knew it hadn’t been. Sherlock was old enough now to know what he was doing.  
  
Mycroft didn’t get much sleep that night.  
  
~  
  
Mycroft had been right: the older Sherlock got the better looking he became.

At fourteen Sherlock was growing like a weed. A weed with pointy elbows, a breaking voice and a gigantic appetite for food and knowledge. He rarely slept, and seemed (to Mycrofts perpetual envy) to be able to consume gigantic meals without gaining so much as a kilo.  
  
He had also discovered masturbation.  
  
Mycroft had walked in on Sherlock four times in the past month. Each time Sherlock had been very nearly entirely naked, his shockingly slim body tense with desire, his fist pumping at his red, swollen cock.  
  
Each time Mycroft had slammed the door shut.  
  
The first time had been an accident, or so he had assumed. The second time could have been an accident too. But three times suggested a pattern to him, and by the forth time he was sure.  
  
He could barely open a door in the house without tensing, now, unsure of what he would see on the other side.

Furthermore, the longer it took for Sherlock to strike, the more wound up Mycroft became. Opening bathroom doors filled him with terror. The laundry wasn’t safe. He would never see the interior of the shed the same way again.  
  
The worst part was the fact that he couldn’t delete what he had seen. It had been so shocking, so intimate, and so damned deliberate, that it refused any kind of denial, removal or eradication in his mind.  
  
Truthfully, he could still remember every detail with vivid clarity. The way the veins had stood out in Sherlocks arms, the shiny red of his foreskin, the way he had looked up, mouth open, eyes fixing on his-  
  
Mycroft felt haunted and, though he repressed the knowledge as best he could, uncomfortable aroused. It was, he knew, some sort of experiment on Sherlocks part. How far he could push his brother, how long would he be able to get away with it…  
  
How far would he take it? Mycroft pondered. How would he react, if he were for some horrible reason unable to escape right away?  
  
He didn’t know. And he hated himself for not knowing.  
  
It was a Friday. Nothing had happened so far. Sherlock had remained fully clothed the entire day, apparently too busy with his homework to bother him. Sherlocks approach to homework was to antagonize his teachers by giving his answers in a complex code. He made up a new one every week.  
  
Mycroft sat in the living room, feeling cautiously peaceful. The fire was crackling and Father was humming to himself as he washed the dishes. Perhaps the experiment was over? Perhaps Sherlock had collected all the required data?  
  
The thought was somehow disappointing. Mycroft internally scolded himself, trying to find the source of the disappointment and kill it. As usual, however, it eluded his best attempts at destruction.  
  
Sherlock went to bed early without saying goodnight. Mycroft examined the code he’d written all the answers to his homework in- an interesting blend of Latin and hieroglyphics.  
  
He spent a few minutes trying to decode it, pleased at how difficult it was. Sherlock, though not as clever as he was, was undoubtedly the smartest person he had yet come across.

Mycroft yawned. It was getting late, and he might as well get to bed. He climbed the steps towards his bedroom, not even thinking about Sherlock.  
  
He opened his bedroom door and stopped dead.  
  
Sherlock was on his bed, utterly naked, two fingers stuffed up his arse, his other hand slowly stroking his leaking cock. Mycroft felt as if he had been hit over the head with something very, very heavy.  
  
He staggered inside, closing the door, terrified of somebody coming upstairs behind him. Sherlock was making soft little moaning noises, his eyes roaming over Mycrofts body.  
  
‘Sherlock-’  
  
‘Mycroft?’ Sherlock asked, breathless. ‘I know you’ve been thinking about it.’  
  
‘Sherlock, this is-’  
  
‘Against the rules?’ Sherlock said, eyes flashing. ‘Or did you only like it when I was seven?’  
  
Mycroft felt his cock twitch, and his cheeks flushed in shame. Had Sherlock, even then, been manipulating him, preparing him, working out how to get them to this point? Had all those innocent touches, those pleading glances…  
  
‘Give me a hand,’ Sherlock pleaded. ‘Mycroft, please…’  
  
Oh god. When had he ever been able to resist Sherlock saying his name, begging him, the word please on his lips?  
  
He sat on his bed and linked his fingers with Sherlocks. His brothers cock twitched at his touch, pre-come leaking from the tip and running down their joined fingers, sticking them together.  
  
‘I’ve got lube,’ Sherlock whispered. ‘Want your fingers in me.’  
  
Mycroft knew he shouldn’t (knew he would, knew he should lock the door) but he nodded. Sherlock withdrew his fingers and passed it over. The wetness of his fingers made Mycroft bite down on his bottom lip to stop himself from making a noise.  
  
He slicked his fingers up as best he could one handed, figuring that Sherlock was already stretched enough by his own fingers for it not to be too much of an issue. Neither of them spoke.  
  
He reached around, finding Sherlocks hole already wet and twitching. Mycroft breathed through his nose, trying to focus on the way Sherlock sounded, and the way their hands moved together. Anything to distract himself from his own aching, aching cock.  
  
He pressed in, both his fingers at once. Sherlock hissed at the stretch, which was slightly more than Mycroft had anticipated it would be. His own fingers were larger than Sherlocks, after all. He hesitated, unwilling to hurt his brother but almost equally unwilling to withdraw from the heat clenching around his fingertips.  
  
‘Don’t s-stop,’ Sherlock said, almost lisping. ‘In, in.’  
  
So Mycroft pushed, feeling the ring of muscle clench and relax a few times around his knuckles before drawing him in. They sighed in unison, Sherlock tightening their grip on his cock.  
  
The angle was awkward, but not so awkward that Mycroft couldn’t lean down and press his lips over Sherlocks. It strained his back, but was worth it for the noise of surprise and pleasure Sherlock made as he opened his mouth.  
  
Their tongues moved together, hungry, Sherlocks breathing now ragged. Eventually he pulled away, eyes dark.  
  
‘Mycroft, I’m not going to last-’  
  
‘Of course you aren’t,’ Mycroft said, smiling. ‘You’re young. You’ll learn. Come for me, let me see it.’  
  
Sherlock closed his eyes. Mycroft twisted his fingers within his brother, brushing over the slight bump of his prostate. Once, twice, three times, and each time Sherlock stopped breathing, until on the forth he came, eyes screwed shut, a low moan caught in his chest.  
  
Mycroft watched, his own cock twitching in sympathy. His fingers ached as Sherlock clamped down around them but he didn’t remove them, not until Sherlocks cock had finally started to soften, and the muscles holding his fingers in relaxed.  
  
Sherlock seemed to melt into the bed, his eyes opening slowly. He smiled, slowly, deep affection in his eyes. Mycroft felt his heart stutter in his chest.  
  
‘Do you want me to do anything?’ Sherlock asked, nodding towards Mycrofts lap. Mycroft shook his head, almost overwhelmed.  
  
‘I’d rather take care of it myself,’ he said, voice soft. ‘Sherlock… what we just did…’  
  
‘It’s ok,’ Sherlock said, leaning up and kissing him on the lips, kissing the words away. ‘It’s ok. We love each other. And if you don’t want to fuck me until I’m eighteen then I’ll wait, I will.’  
  
Mycroft closed his eyes. Sherlock rested his head on Mycrofts shoulder. They sat like that for a long time, the silence of the house reassuring Mycroft that nobody had realized what had happened between them. Every rational cell in his brain was telling him to withdraw immediately, to save them both from years of pain and confusion. But it seemed impossible to him that being with Sherlock like this could cause pain or confusion.  
  
He realized that the hot, trembling feeling in his heart might in fact be love.  
  
‘Oh Sherlock,’ Mycroft whispered at last. ‘What on earth are we going to do?’  
  
‘We’re clever,’ Sherlock said, and Mycroft could hear the smile in his voice. ‘We’ll work it out.’  
  
Mycroft nodded, taking Sherlocks chin in his hand and tilting his face until he could look into his eyes. He saw peace, and lust, and trust all mingled together in his brothers eyes.  
  
With a sigh, Mycroft leant down and kissed him again.  
  
They were clever. They’d work something out.

**Author's Note:**

> You can send me a prompt on my tumblr- I love rare pair fic :)
> 
> raregloves.tumblr.com


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